Did I mention that 2008 is the Year of the Frog? Well, believe it or don’t, another major conservation effort directed at the world’s amphibians kicks off in January 2008, and in an effort to bring all you wonderful Tet Zoo readers up to speed on amphibian diversity before it launches, we need to get through ALL of the world’s amphibian groups first. But that’s not as bad as it sounds. Besides anurans – which we’ve nearly covered in entirety – there are only two other groups, and here we look in detail at one of them.

With apologies to those who already have privileged knowledge…. if I told you that there was a group of living tetrapods that have sensory tentacles, sometimes sport protrusible eyes, sometimes lack eyes entirely, often exhibit sophisticated parental care and may even feed their babies on a specially grown layer of nutritious epidermal skin, are incredibly long-bodied yet often lack tails, and sometimes possess large, anatomically complex, eversible male sexual organs, you might wonder which recreational drugs I was taking. The fact is, I’m talking about a very real – albeit very poorly known – group of living tetrapods: the caecilians.

All extant caecilians (pronounce it ‘say-see-lee-un’) are long-bodied, limbless, superficially worm-like amphibians with reduced eyes. They are predominantly fossorial (adapted for burrowing), although some are aquatic or semiaquatic and some terrestrial species have aquatic larvae. Limb girdles are entirely absent and skin folds (annulae) encircle the body. Despite their mostly fossorial habits some species are visually striking, being blue, purple, green, bright orange, yellow, or with bright yellow lateral stripes [image of bright orange caeciliid Schistometopum thomense from the Gulf of Guinea shown below]. Others are decorated with blotches, or have a head that is lighter in colour than the body. Poison glands are present (some species may even be quite toxic to humans), so it’s likely that the bright colours are aposematic. While the smallest species (like the caeciliid Idiocranium russelli from Cameroon) are mature at just 70 mm, the largest – the very slender-bodied Caecilia thompsoni from Colombia – reaches 1.5 m [C. thompsoni shown in adjacent image; photo by Taran Grant].

In the most primitive living caecilians (the South American rhinatrematids), a short tail is present and the mouth is located at the front of the head; in the more advanced groups no tail is present and the mouth is situated further back, slung underneath the head. It’s mostly assumed that caecilians are generalist predators of soil invertebrates such as earthworms, ants and termites – animals that have been termed ‘soil ecosystem engineers’ by ecologists. However, it’s also been argued that some caecilians are specialists (preying specifically on termites, earthworms or beetle pupae), or even detritivores, ingesting leaf humus and other plant fragments (Hebrard et al. 1992). This last proposal would be radical given that amphibians are essentially all carnivorous as adults, and a later study showed that soil and detritus recovered from the gut contents of the species concerned (the east African caeciliid Boulengerula taitana) originated from its earthworm prey (Gaborieau & Measey 2004). Small vertebrates including frogs, lizards, burrowing snakes (Presswell et al. 2002) and possibly rodents sometimes fall prey to the larger species. Caecilians themselves are preyed upon by burrowing snakes, fish (Gazola Da Silva et al. 2007), and by introduced animals like chickens, pigs and the tenrecs that have been introduced to the Seychelles.

Caecilians occur throughout the humid tropical regions of the world: in South America, equatorial eastern and western Africa, and tropical Asia including the Philippines and the western Indo-Australian archipelago. They also inhabit the Seychelles. The absence of caecilians from central equatorial Africa and Madagascar is odd and we should consider the possibility that they might await discovery in these areas. Generally assumed to be rare and highly elusive, some studies have shown that at least some caecilian species can be abundant if searched for (Measey 2004), and in fact present in sufficient numbers to be (presumably) ecologically significant, especially so given their effects on soil ecosystem engineers (Jones et al. 2006).

It stands to reason that, because of their fossoriality, we know relatively little about caecilians, and because many species are poorly known and poorly represented in zoological collections, confusion about their systematics and taxonomy has been rife. A nice example is provided by the tropical American caeciliid Gymnopis* syntrema: in a paper subtitled ‘a comedy of errors’, Nussbaum (1988) argued that ‘six different binomial names have been applied to this species; it has been assigned to seven genera, two subfamilies of a single family, and three families’ (p. 921). Currently, 33 genera and about 175 caecilian species are recognised, so this isn’t a huge group. Until 1968 all caecilians were united in one ‘family’ – Caeciliidae** – but later work by Edward H. Taylor (read on) and Ronald A. Nussbaum proposed that this should be divided into six ‘families’ (Rhinatrematidae, Ichthyophiidae, Uraeotyphlidae, Scolecomorphidae, Caeciliidae and Typhlonectidae). Multiple other families and other suprageneric groups were recognised by a few authors during the 1980s, but were later rejected as artificial or erroneous (Nussbaum & Wilkinson 1989). Frost et al. (2006) argued for a new classification where only three ‘families’ are recognised, but in a major recent review Wilkinson & Nussbaum (2006) continued to use all six.

* Not a typo, though of course some workers have inadvertently spelt it Gymnophis [sic].

** Little known is that a family of psocopteran insects has also been called Caeciliidae, and it was recommended by the ICZN that the caecilian group therefore go by the older spelling Caeciliaidae (psocopterans are booklice, bookflies and so on. I keep lots of them in my office). Nussbaum & Wilkinson (1989) argued that this decision was inappropriate because Rafinesque, the author of Caeciliaidae, never associated any generic name with this group (he only named it for an Italian vernacular name: ‘Ceciliani’), nor did he specify its intended content. Despite these objections, Nussbaum & Wilkinson (1989) continued to use Caeciliaidae following the ICZN’s ruling, although other authors did not. In 1996 the ICZN changed the ruling such that Caeciliidae became reinstated for the amphibians; the alternative name Caeciliusidae is now used for the psocopterans (Wilkinson & Nussbaum 2006). A caeciliusid is shown in the adjacent image – perhaps the only non-tetrapod I’ve featured so far on Tet Zoo.

There are very few good non-technical sources where you can read up on caecilians: the only one I can readily recommend is Nussbaum (2000). A major volume devoted entirely to caecilians, Taylor’s 1968 848-pp The Caecilians of the World: A Taxonomic Review, is cited in just about every bit of caecilian literature and proved instrumental in initiating new interest in the taxonomy and phylogeny of the group. I thought about getting hold of a copy recently, but gave up when I discovered that it can’t be obtained for less than £138 ($275). A German book, Die Blindwühlen, was published on the group in 1996 (Himstedt 1996), and a French one – Les Gymnophiones, ces curieux Amphibiens – in 2000 (Exbrayat 2000) [image above shows someone’s pet Ichthyophis].

Tentacles and protrusible eyes

In some details, caecilian anatomy is surreal. Easily the weirdest features have to be the tentacles: unique to the group, these are paired sensory structures that emerge from a cavity on the side of the snout between the eye and nostril. They are always quite easy to see, even in the smallest species (in the image above of a captive Ichthyophis, you can see the pale tip of the retracted tentacle half-way between the eye and nostril). No other tetrapod has anything like this. Derived from the tear duct, extrinsic eye muscles and other orbital structures, the tentacles are connected to the vomeronasal organs and presumably allow the animals to test their environment for sensory clues.

The caecilian skull is generally bullet-shaped, robust, thick-boned and with strongly adhering skin [adjacent image, showing the skull of the American caeciliid Dermophis mexicanus, is from DigiMorph]. Their recurved teeth are sometimes sharp-keeled and bicusped (but wait for part II). The eyes of caecilians are sometimes visible beneath the skin and set within bony sockets (e.g., Ichthyophis), are sometimes hidden beneath the bones of the skull (e.g., Scolecomorphus), and are sometimes completely absent (e.g., Boulengerula). While the tentacle is often located close to the nostril and some distance from the eye, the eye and tentacle are close in position in some species. Scolecomorphids, containing only Scolecomorphus and Crotaphatrema, are unique to equatorial Africa and have a particularly large tentacular opening located near the tip of the snout, ahead of the under-slung mouth. The close position of the eye and tentacle mean that they’ve become connected: in its resting position, the eye is located beneath the lateral surface of the skull, but full extrusion of the tentacle causes the eye to move out of the skull and down the tentacle (O’Reilly et al. 1996). An area of the tentacle lacking in pigmentation presumably allows light to reach the retina. Scolecomorphids are the only tetrapods that can deliberately move their eyes out of their skulls. Scolecomorphids are also unusual in lacking a stapes.

Caecilians are also unique in that they have two sets of jaw-closing muscles: in addition to the adductor mandibulae muscles that are located at the back of the jaws, they also use their interhyoideus posterior muscles in jaw closure. These muscles are located in the neck and are attached to the retroarticular process at the posterior end of the lower jaw: they close it by pulling down and backwards on the retroarticular process (Nussbaum 1983). Other tetrapods possess interhyoideus posterior muscles, but they aren’t used in jaw closing, so why have caecilians co-opted them for this use? The answer might be that, in evolving a rigid, box-like skull specialised for burrowing, caecilians have had to reduce and close the temporal fossae that originally housed the adductor mandibulae muscles. To compensate for the weakened power provided by the now reduced adductor mandibulae, caecilians have switched to using the interhyoideus posterior as well – a classic example of exaptation (where an existing structure is co-opted for a new function) [adjacent image, from Wilkinson & Nussbaum (2006), shows the variation in caecilian cranial and interhyoideus posterior morphology].

Of course, this isn’t where it ends – we still have the weird sexual organs to look at yet, plus the stegokrotaphy, zygokrotaphy, the whole ‘out of India’ thing, the viviparity, dermatotrophy and matrotrophy, and the biggest lungless tetrapod ever (the bizarre Atretochoana, shown at the very top of the article). Be sure to tune in to the next thrilling installment of Tetrapod Zoology!

Wow I thought I knew alot about these guys but theres a few bits I had no clue on (the no tail bit) Talking of ‘tails’, Im sitting here looking at one of my caecilians stick its head in my filter outlet I can see the small white patch on the underside of the tip of the rear end of the body. Any ideas what that is?

This animals are really cool and doubtless among the strangest tetrapods we know. Some time ago I really thought about buying one from a local zoo-store, but my aquarium is most probably not big enough for them, and as they burrow in the ground, the stones I use as decoration could easily fall, so I did not buy one. But hell, they were so strange that I watched them for about 15min again and again. If they emerge from the ground to breath air on the surface they just look like miniature space slug hunting for millenium falcons.
This animals are often portrayed as being comparably slow and worm-like and therefore only able to catch slow prey, but some years ago I read an article about one which ate all small guppies in an aquarium.
Another very good book which covers ceacillians as well as many other very poorly known aquatic amphibians is “Amphibien im Aquarium” from Hans-Joachim Herrmann.
BTW, from what are nerd-pills made? At Ankh-Morpok dried frogs are used, so why not try dried ceacillians?

Two questions, though. First, could you not find a better photo of the alleged tentacles than a head with a vague white spot? It would be great to see the extruded eyeballs in action. And second, what does it mean for a caelician, or any legless animal, to be “tailless”? My naive perspective of “that which sticks out back behind the pelvis” is obviously no use here. Is it to do with absence of ribs?

Thanks David (and everyone else). On phylogenetic analysis of the whole group, Wilkinson is working on this I think, but meanwhile have you seen Wilkinson & Nussbaum (2006)? I agree with these authors, by the way, that Apoda is a dumb name for the group and that Gymnophiona should be used for the crown-group, despite suggestions from some (e.g., Trueb & Cloutier 1991) that Apoda should be used for the crown and Gymnophiona for the stem.

Regarding Eocaecilia, Rubricacaecilia, pantylid microsaurs and so on… in a major effort to get the caecilian text finished, I made a strenuous effort to avoid discussing fossil taxa and caecilian origins and relationships, but I suppose I’ll be coming back to this at some stage (I have to do albanerpetonids after all). If you can’t wait until then see the old DML post here.

Finally, when will you people understand that tetrapod does not mean ‘it has four legs’? It’s just the label for a clade, the ancestral state for which is to possess four limbs. Yeah, I know, you were joking

Something I had forgot to say: Pugs are breeded to have a flat face and big eyes in a very massive way. The result is that their orbitas are very conical and give the eye nearly no hold. Sometimes only a little shake has the effect that the eye can spring out of the skull.

Two questions, though. First, could you not find a better photo of the alleged tentacles than a head with a vague white spot? It would be great to see the extruded eyeballs in action. And second, what does it mean for a caelician, or any legless animal, to be “tailless”? My naive perspective of “that which sticks out back behind the pelvis” is obviously no use here. Is it to do with absence of ribs?

Hi Mike. NO – I could not (to my frustration) find any good pics of the tentacles on the web. There are lots in the literature, but none that I could steal/borrow. I was particularly surprised to find that there are no good images on the web of a Scolecomorphus extending its eye down its tentacle – I had assumed that this might have made the science news back when it was published (1996).

A tail is that part of the body that sticks out posterior to the cloaca, the end of the gut (there’s no pelvis in crown-group caecilians so its position in the group can’t help us). Basal caecilians do have a true tail (and even then it’s short, consisting only of 4-12 vertebrae), but the derived teresomatans don’t: the cloaca is at the posterior end of the body and they really have lost the tail. More on this in the next post, to appear later today I think.

Incidentally, many snakes also have a surprisingly short tail. In fact (as a generalisation) long-bodied tetrapods tend to have elongated their bodies, with necks and tails not being that important.

I agree with these authors, by the way, that Apoda is a dumb name for the group and that Gymnophiona should be used for the crown-group, despite suggestions from some (e.g., Trueb & Cloutier 1991) that Apoda should be used for the crown and Gymnophiona for the stem.

I absolutely disagree. All except two or three papers have used Apoda for the crown-group and Gymnophiona for the total group. The only reason not to use Apoda is that Apoda was originally coined as a family and therefore unavailable under the ICZN for above-family-group nomenclature, but firstly, this would make Urodela unavailable as well (most common usage: Urodela — crown; Caudata — total group), secondly, it’s a silly rule that doesn’t serve any tangible purpose, and thirdly, we enlightened users of rankless nomenclature need not care about it anyway.

Sure, based on its meaning, Apoda is a stupid name, but so are lots of others. Plus, so far it fits: the crown-group is footless, while Eocaecilia was not.

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Yay! Albanerpetontids!

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Don’t post on McGowan (2002) just yet. Its cladogram is so weird that Michel and I decided to have a look at the teensy data matrix and to write a paper about it. Something like half of the matrix consists of mistakes (this is not an exaggeration), the limits between the states of continuous characters are never (yes, never) explained, McGowan doesn’t seem to have known that it’s not necessary to code the most plesiomorphic state as 0 and therefore made up an all-zero ancestor and ordered a character in a loop, and so on. In short, we redid the matrix and get much more conventional results. The paper is submitted and presumably in review right now.

Well, a complete opposite of short-tailed but long-bodied tetrapods would be the Pygopodidae, whose tails are actually very long. But that´s perhaps because they do climb comparably often in vegetation, whereas most other long-bodied reptiles or amphibians are either completely terrestrial, subterrestrial or amphibic.

Sordes, thanks for inventing a new direction to breed pugs. If it succeeds, I may even become interested in pugs. Stalk-eyed pug and maybe even propulsive-eyed dog. Please, please, get some breeders interested!

Did anybody find how long ago caecilian tree diversified? Or, more specifically – how many clades of caecilians and other tetrapods survived KT extinction? It seems, that fossorial, freshwater and insectivorous clades survived KF in large numbers- that is, not just “frogs” and “turtles” survived KT, but very many clades of frogs and turtles.

Sounds a bit against theories that KT extinction was associated with acid rains and suchlike events to which amphibians are highly vulnerable.

Response to David on Apoda vs Gymnophiona… I never thought I’d hear myself saying this, but, given that neontologists who work on caecilians have been pretty consistent in using Gymnophiona for the limbless, girdle-less crown group, we would make them look silly if we enforced use of Gymnophiona for the limbed, girdle-possessing stem forms (hey, I sound like Walter Joyce). All statements defining gymnophionans as limbless, girdle-less, tentacle-possessing animals would be wrong. Yes, most papers which cover the stem forms have used Gymnophiona for the total group, and Apoda for the crown, but that doesn’t mean this is the system we should adopt (nor are we talking about that many papers anyway).

The main problem I have with Apoda isn’t necessarily that it would be inappropriate for use of the total-group (which it would be), but that it’s one of the those dumb names – like Sauria or Vermes – which has been widely applied to assorted members of Animalia. There’s a moth called Apoda for example (and it was named in 1809, three years before the term was applied to caecilians). See Wilkinson & Nussbaum (2006), pp. 52-53: two of the leading world experts on caecilians, both of whom have published tens more papers on this group than those who have used Gymnophiona for the total-group, and they both argue that they want to stick with Gymnophiona for the crown. I say we should listen to them. And yes, Gymnophiona means ‘naked snakes’ and hence is not exactly inappropriate for the caecilian crown. Maybe the total-group should be called Pan-Gymnophiona or some such.

Many thanks David for the heads-up on the response to McGowan 2002: I’ll be very interested in seeing that paper when it appears. Good luck with it.

Martin R: I wondered about the same thing. From what I’ve found online, it seems they weren’t named after an Italian vernacular name. Rather, Rafinesque introduced “Ceciliani” as a vernacular name for them (based on the generic name Caecilia) in a publication apparently written in Italian in 1814. (He lived in Sicily then.) I looked up his 1815 book “Analyse de la Nature” on gallica.bnf.fr and in it, he doesn’t use that name, but classifies the genera Caecilia and Amphisbaena together in a family Gymnodermia. The generic name Caecilia (derived from caecus, Latin for blind?) goes back at least to Linnaeus, and already appears in the 6th edition of the Systema naturae (published 1748).

You may well have read this already but I thought it might be of interest. From Animal Treasure by Ivan Sanderson, copyright 1937.

“Chasing a giant mite under the matted grass roots, I laid bare a small cavern about the size of a man’s fist, in which stood a small mound of pyramidal form like a miniature volcano. On top of this was coiled a very small caecilian, purple in color and no larger than an earthworm. As I opened its little home, its flat snake-like head came round towards me and it spat a small blob of water at me with considerable force. This is what it continued to do while I gathered it up.

It had been tightly coiled up; when removed, it revealed half a dozen crystal-clear and perfectly spherical eggs tied into a knot by tough, slender horny cords growing out of both opposing ends. These were perched on the top of the mound and were being brooded by their mother. The eggs, of a greater diameter than the mother herself, contained minute replicas of herself completely sealed up within. These whizzed round and round when the eggs were touched.”

There’s a bit more about this and another species on the next couple of pages…

But jeez. Do caecilian’s often spit defensively? And those eggs… is that kind of structure as weird as it sounds?

(As an aside, a childhood of reading people like Sanderson and Willy Ley and the delightfully goony Bernard Heuvelmans set me up to appreciate Tetropod Zoology. Thanks for one of my favorite websites.)

Frost et al. (2006) made up the name Parabatrachia for it. Considering the instability of the position of the albanerpetontids, this might not be as bad an idea as I used to think, although Parabatrachia is branch-based while Batrachia is node-based…

Did anybody find how long ago caecilian tree diversified? Or, more specifically – how many clades of caecilians and other tetrapods survived KT extinction?

The Late Cretaceous and Cenozoic fossil record of caecilians consists only a few isolated vertebrae that may or may not belong to the crown-group. The Early Cretaceous record consists only of Rubricacaecilia, which is outside the crown-group, and the only earlier record is Eocaecilia.

There are of course a few molecular divergence date estimates; all of them are very old (Triassic or Permian), but most of them are miscalibrated, and, as I just mentioned, an internal calibration is not possible.

It seems, that fossorial, freshwater and insectivorous clades survived KF in large numbers- that is, not just “frogs” and “turtles” survived KT, but very many clades of frogs and turtles.

Sounds a bit against theories that KT extinction was associated with acid rains and suchlike events to which amphibians are highly vulnerable.

No, you only need a few individuals of very few species buried in calcareous soil or maybe even living in carbonate-rich water.

… two of the leading world experts on caecilians, both of whom have published tens more papers on this group than those who have used Gymnophiona for the total-group, and they both argue that they want to stick with Gymnophiona for the crown. I say we should listen to them. […] Maybe the total-group should be called Pan-Gymnophiona or some such.

Their loss of the stapes is derived, rather than primitive (other, more primitive caecilians possess a stapes). In fact a stapes is primitive for Tetrapoda, so its absence in any member of the group has to be an advanced one, not a primitive one.

Well, survival MIGHT mean survival of just few individuals, but it changes nothing. Small colonies of dinosaurs didn’t survive worldwide.

Many small mammal lineages survived and apparently very many lineages of birds. At least five crocodilian lineages survived.

Birds, as a rule, don’t hibernate, are very suspectible to air poisoning, cannot starve for long and don’t hide, but react to danger by flying. As I said, amphibians are very suspectible to acid rain or any water pollution.

Dinosaurs, as big animals, are very resistant to many dangers. They can live off fat reserves longer, can survive a pause of many years of non reproduction, withstand air pollution better. Nevertheless, all dinosaur lineages – even small and pretty birdlike forms – died out.

Modern theories about K/T ignore or distort above facts about biology of surviving/extinct tetrapods.

If dominant forces were: cold, acidic/sulphuric pollution, burst of heat radiation, air pollution by particles raised by impact – K/T would result in (almost) total bird and amphibian extinction and dinosaur survival.

So – environmental events during K/T impact were very different than imagined today.

Many small mammal lineages survived and apparently very many lineages of birds.

Probably very few of either. (Remember that there’s no evidence of placentals or marsupials in the K.)

cannot starve for long

Seed-eaters wouldn’t need to starve in the first place.

and don’t hide, but react to danger by flying.

That depends. Paleognaths, galliforms and anseriforms often don’t do that.

Also remember that most bird lineages did die out! The entirety of Enantiornithes, for example.

Dinosaurs, as big animals, are very resistant to many dangers.

Big animals cannot hide from a fire. They are in danger from the impact itself (which, being an earthquake, may have thrown all large terrestrial animals in North America to the ground). Furthermore, terrestrial big animals cannot live off seeds or insects, they depend on green plant parts; as soon as all green plant parts are destroyed (by fire and acid rain), the food chain they are parts of collapses.

It may interest you that, unlike earlier and later ones, leaves from the earliest part of the Paleocene are almost devoid of insect damage. Looks like lots of herbivorous insects died out, too.

Modern theories about K/T ignore or distort above facts about biology of surviving/extinct tetrapods.

Are these homologous but all non-analogous sensory structures?
Nasal-orbital tentacles of caecillians
Barbels of catfish
Fleshy barbels of star faced moles
Vibrissae of rodents, cats
IIRC some beak feathers in some birds(?)

Is it possible that antlers and/or horns were initially eyebrow feelers/vibrissae that eventually became enlarged and ossified or keratinized, rather than initially being mere eyeshades or eye protection (or ice age snow shovels)?

[quote]Probably very few of either. (Remember that there’s no evidence of placentals or marsupials in the K.)[/quote]

Molecular tree branching.

[quote]Seed-eaters wouldn’t need to starve in the first place.[/quote]

Lineages which survived were almost exclusively insect-eaters.

And either I missed something, but small seeds and seed-eating fauna (like rodents or finches) were not common during K/T. You need to wait until mid-Tertiary and first grasslands.

[quote]Also remember that most bird lineages did die out! The entirety of Enantiornithes, for example[/quote]

Again – but ALL dinosaurs.

[quote]Big animals cannot hide from a fire.

as soon as all green plant parts are destroyed (by fire and acid rain), the food chain they are parts of collapses.[/quote]

Yes they can. They can go into water. And have fat reserves. Plants regrow after fire. Modern ungulate can survive few weeks of no food. Rodent cannot. I wonder how long could a grown hardosaur or ceratopsian survive?

[quote]Think again.[/quote]

I suggest looking at modern wildfires. On African savanna, they anihillate small ground fauna, while ungulates actually benefit from better grazing. On wildfires in Russian taiga, suffocated birds litter the ground.

Is it possible that antlers and/or horns were initially eyebrow feelers/vibrissae that eventually became enlarged and ossified or keratinized, rather than initially being mere eyeshades or eye protection (or ice age snow shovels)?

No. Hairs cannot become bones.

As for their origins, consider sexual selection.

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Jerzy, only HTML works here: <blockquote>.

Molecular tree branching.

Depends on the calibration. Most published molecular divergence date estimates are mis- or at least undercalibrated. (I’ve published on this.)

Lineages which survived were almost exclusively insect-eaters.

Details, please. Paleognaths and galliforms can live off seeds — and many insects are supposed to have survived, just not those that depend on green plant parts.

And either I missed something, but small seeds and seed-eating fauna (like rodents or finches) were not common during K/T.

You forgot the acid rain, and the perturbation of the water cycle, and so on…

Modern ungulate can survive few weeks of no food. Rodent cannot.

A rodent can hibernate, and it can store seeds in its burrow.

I wonder how long could a grown hardosaur or ceratopsian survive?

As long as it takes for the shock wave to reach it and throw it over, probably…

I suggest looking at modern wildfires.

That’s not enough. An impact does not only trigger a fire.

On African savanna, they anihillate small ground fauna,

What about burrowing fauna?

On wildfires in Russian taiga, suffocated birds litter the ground.

See? Most birds, including apparently all arboreal ones, died out.

It has been suggested that all birds outside of Antarctica died out. This makes some biogeographic sense, but the Antarctic fossil record is too poorly known at present to test this. Vegavis, the only certain K neornithean, is from there, though.

You see, I accept there was “some” acid rain. But scenario where it is decisive factor goes against relative sensitivity of different groups.

I wonder how long could a grown hardosaur or ceratopsian survive?

As long as it takes for the shock wave to reach it and throw it over, probably…

Shock wave, air blast etc. were severe continent-wide, but too weak to kill dinosaurs worldwide – not according to estimates of impact. Not to say how earthquake affect animals in burrows.

I would say that decisive factor was blocking of photosynthesis for several months to several years. For long enough to starve surviving dinosaurs. But all surviving land tetrapods can subsist on detritus-eating invertebrates and fungi (land tortoises).